Semiconductor device

ABSTRACT

A semiconductor device includes a pillar-shaped semiconductor having an impurity concentration of 10 17  cm −3  or less. A first insulator surrounds the pillar-shaped semiconductor and a first metal surrounds a portion of the first insulator at a first end of the pillar-shaped semiconductor. A second metal surrounds a portion of the first insulator at a second end of the pillar-shaped semiconductor, and a third metal surrounds a portion of the first insulator in a region between the first and second metals. A second insulator resides between the first metal and the third metal, and a third insulator resides between the second metal and the third metal. The first metal is electrically connected to the first end of the pillar-shaped semiconductor, and the second metal is electrically connected to the second end of the pillar-shaped semiconductor. The third metal has a work function of about 4.2 eV to about 5.0 eV.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/160,788, filed Jan. 22, 2014, which claims the benefit of the filingdate of Provisional U.S. Patent Application Ser. No. 61/756,677 filed onJan. 25, 2013. The entire content of this application is herebyincorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for producing a semiconductordevice and a semiconductor device.

2. Description of the Related Art

The degree of integration of semiconductor integrated circuits, inparticular, integrated circuits using MOS transistors has beenincreasing. With the increasing degree of integration, the size of MOStransistors used in integrated circuits has been decreased to nano-scaledimensions. Such a decrease in the size of MOS transistors causesdifficulty in suppressing leak currents, which poses a problem in thatit is hard to reduce the area occupied by the circuits because of therequirements of the secure retention of necessary currents. To addressthe problem, a surrounding gate transistor (hereinafter referred to as“SGT”) having a structure in which a source, a gate, and a drain arearranged vertically with respect to a substrate and a gate electrodesurrounds a pillar-shaped semiconductor layer has been proposed (See forexample, Japanese Unexamined Patent Application Publication Nos.2-71556, 2-188966, and 3-145761).

As the width of a silicon pillar decreases, it becomes more difficult tomake an impurity be present in the silicon pillar because the density ofsilicon is 5×10²²/cm⁻³.

It has been proposed in known SGTs that the channel concentration isdecreased to be a low impurity concentration of 10¹⁷ cm⁻³ or less and athreshold voltage is determined by changing the work function of a gatematerial (See for example, Japanese Unexamined Patent ApplicationPublication No. 2004-356314).

It is disclosed that, in planar MOS transistors, the sidewall of an LDDregion is formed of a polycrystalline silicon having the sameconductivity type as a low-concentration layer, surface carriers of theLDD region are induced by the difference in work function, and thus theimpedance of the LDD region can be reduced compared with LDD MOStransistors with an oxide film sidewall (See for example, refer toJapanese Unexamined Patent Application Publication No. 11-297984). It isalso disclosed that the polycrystalline silicon sidewall is electricallyinsulated from a gate electrode. The drawings show that thepolycrystalline silicon sidewall is insulated from a source and a drainby an interlayer insulating film.

BRIEF SUMMARY

It is an object of the disclosure to provide an SGT having a structurein which a transistor is formed by using a difference in the workfunction between a metal and a semiconductor.

A semiconductor device according to an aspect of the disclosure includesa pillar-shaped semiconductor having an impurity concentration of 10¹⁷cm⁻³ or less, a first insulator that surrounds the pillar-shapedsemiconductor, a first metal that surrounds a portion of the firstinsulator at a first end of the pillar-shaped semiconductor, a secondmetal that surrounds a portion of the first insulator at a second end ofthe pillar-shaped semiconductor, a third metal that surrounds a portionof the first insulator in a region sandwiched between the first metaland the second metal, a second insulator formed between the first metaland the third metal, a third insulator formed between the second metaland the third metal, wherein the third metal has a work function of 4.2eV to 5.0 eV.

The semiconductor may be silicon.

The first metal and the second metal may have a work function of 4.0 eVto 4.2 eV.

The first metal and the second metal may have a work function of 5.0 eVto 5.2 eV.

According to the present disclosure, there can be provided an SGT havinga structure in which a transistor is formed by using a difference inwork function between metal and silicon.

Carriers are induced by a difference in work function between metal andsilicon because of the presence of a first metal that surrounds aportion of a first insulator at a first end of a pillar-shaped siliconand a second metal that surrounds a portion of the first insulator at asecond end of the pillar-shaped silicon. Therefore, when the first metaland the second metal have a work function of 4.0 eV to 4.2 eV, an n-typetransistor is provided. When the first metal and the second metal have awork function of 5.0 eV to 5.2 eV, a p-type transistor is provided. Thisenables transistor operation despite the lack of an impurity in apillar-shaped silicon. Accordingly, impurity implantation for forming adiffusion layer is not necessary.

A semiconductor device according to an aspect of the present disclosureincludes a pillar-shaped semiconductor, a first insulator surroundingthe pillar-shaped semiconductor, a first metal surrounding a portion ofthe first insulator at a first end of the pillar-shaped semiconductor, asecond metal surrounding a portion of the first insulator at a secondend of the pillar-shaped semiconductor, a third metal surrounding aportion of the first insulator in a region sandwiched between the firstmetal and the second metal, a second insulator between the first metaland the third metal, a third insulator between the second metal and thethird metal, a fourth metal connecting the first metal and the first endof the pillar-shaped semiconductor, and a fifth metal connecting thesecond metal and the second end of the pillar-shaped semiconductor.

Charge carriers are induced at the first end of the pillar-shapedsemiconductor by a difference in the work function between thepillar-shaped semiconductor and the first metal, and charge carriers areinduced at the other end of the pillar-shaped semiconductor by adifference in the work function between the pillar-shaped semiconductorand the second metal.

In a further aspect of the disclosure, it is not necessary that themetals and insulators surround a portion the underlying structure. Thedisclosed device can be realized where the metal or insulator surroundsonly a part of a portion of the underlying structure. A semiconductordevice according to the further aspect of the disclosure includes apillar-shaped semiconductor, a first insulator surrounding a portion ofthe pillar-shaped semiconductor at a first end of the pillar-shapedsemiconductor, a first metal surrounding the first insulator, a fourthinsulator surrounding a portion of the pillar-shaped semiconductor at asecond end of the pillar-shaped semiconductor, a second metalsurrounding the fourth insulator, a fifth insulator surrounding aportion of the pillar-shaped semiconductor in a region sandwichedbetween the first metal and the second metal, a third metal surroundingthe fifth insulator, a second insulator between the first metal and thethird metal, a third insulator between the second metal and the thirdmetal, a fourth metal connecting the first metal and the first end ofthe pillar-shaped semiconductor, and a fifth metal connecting the secondmetal and the second end of the pillar-shaped semiconductor.

Charge carriers are induced at first end of the pillar-shapedsemiconductor by a difference in the work function between thepillar-shaped semiconductor and the first metal, and charge carriers areinduced at the second end of the pillar-shaped semiconductor by adifference in the work function between the pillar-shaped semiconductorand the second metal.

A semiconductor device according to the further aspect of the presentinvention includes a pillar-shaped semiconductor, a first insulator thatsurrounds at least a part of a portion of the pillar-shapedsemiconductor at a first end of the pillar-shaped semiconductor, a firstmetal surrounding at least a part of the first insulator, a fourthinsulator surrounding at least a part of a portion of the pillar-shapedsemiconductor at the second end of the pillar-shaped semiconductor, asecond metal surrounding at least a part of the fourth insulator, afifth insulator surrounding at least a part of a portion of thepillar-shaped semiconductor in a region sandwiched between the firstmetal and the second metal, a third metal that surrounds at least a partof the fifth insulator, a second insulator between the first metal andthe third metal, a third insulator between the second metal and thethird metal, a fourth metal that connecting the first metal and thefirst end of the pillar-shaped semiconductor, and a fifth metalconnecting the second metal and the second end of the pillar-shapedsemiconductor.

Charge carriers are induced at the first end of the pillar-shapedsemiconductor by a difference in the work function between thepillar-shaped semiconductor and the first metal, and charge carriers areinduced at the second end of the pillar-shaped semiconductor by adifference in the work function between the pillar-shaped semiconductorand the second metal.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1( a) illustrates a perspective view illustrating a semiconductordevice according to an embodiment of the disclosure and FIG. 1( b)illustrates a sectional view of the semiconductor device taken alongplane X-X′ of FIG. 1( a).

FIG. 2( a) illustrates a perspective view illustrating a semiconductordevice according to an embodiment of the disclosure and FIG. 2( b)illustrates a sectional view of the semiconductor device taken alongplane X-X′ of FIG. 2( a).

FIG. 3( a) illustrates a perspective view illustrating a semiconductordevice according to an embodiment of the disclosure and FIG. 3( b)illustrates a sectional view of the semiconductor device taken alongplane X-X′ of FIG. 3( a).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor device having an SGT structure according to anembodiment of the disclosure will now be described with reference toFIG. 1.

A pillar-shaped silicon 101 having an impurity concentration of 10¹⁷cm⁻³ or less, a first insulator 102 that surrounds the pillar-shapedsilicon 101, a first metal 104 that surrounds a portion of the firstinsulator 102 at one end of the pillar-shaped silicon 101, a secondmetal 105 that surrounds a portion of the first insulator 102 at theother end of the pillar-shaped silicon 101, a third metal 103 thatsurrounds a portion of the first insulator 102 in a region sandwichedbetween the first metal 104 and the second metal 105, a second insulator107 formed between the first metal 104 and the third metal 103, a thirdinsulator 106 formed between the second metal 105 and the third metal103, a fourth metal 108 that connects the first metal 104 and the oneend of the pillar-shaped silicon 101, and a fifth metal 109 thatconnects the second metal 105 and the other end of the pillar-shapedsilicon 101 are disposed on a substrate 110. The third metal 103 has awork function of about 4.2 eV to about 5.0 eV.

In operation the same potential is applied to the first metal 104 andfirst end of the pillar-shaped silicon 101 because of the presence ofthe fourth metal 108.

Similarly, in operation the same potential is applied to the secondmetal 105 and the second end of the pillar-shaped silicon 101 because ofthe presence of the fifth metal 109.

Therefore, charge carriers are induced by a difference in the workfunction between metal and silicon at the first end and the second endof the pillar-shaped silicon 101.

When the work function of the first metal 104 and the second metal 105is in the range of about 4.0 eV to about 4.2 eV, which is close to awork function of n-type silicon of 4.05 eV, the first end and the secondend of the pillar-shaped silicon 101 function as n-type silicon. Thefirst metal 104 and the second metal 105 are preferably, for example, acompound (TaTi) of tantalum and titanium or tantalum nitride (TaN).

When the work function of the first metal 104 and the second metal 105is in the range of about 5.0 eV to about 5.2 eV, which is close to awork function of p-type silicon of 5.15 eV, the first end and the secondend of the pillar-shaped silicon 101 function as p-type silicon. Thefirst metal 104 and the second metal 105 are preferably, for example,ruthenium (Ru) or titanium nitride (TiN).

In this case, when the work function of the third metal 103 is in therange of about 4.2 eV to about 5.0 eV, the semiconductor device canoperate as an enhancement-type transistor.

When the work function of the first metal 104 and the second metal 105is in the range of about 4.0 eV to about 4.2 eV, which is close to awork function of n-type silicon of 4.05 eV, the first end and the secondend of the pillar-shaped silicon 101 function as a source and a drain ofan n-type silicon. A portion of the pillar-shaped silicon 101 surroundedby the third metal 103 functions as an intrinsic-type (i-type) silicon,low-concentration n-type silicon, or low-concentration p-type silicon.Thus, an n-type transistor is provided.

When the work function of the first metal 104 and the second metal 105is in the range of about 5.0 eV to about 5.2 eV, which is close to awork function of p-type silicon of 5.15 eV, the first end and the secondend of the pillar-shaped silicon 101 function as a source and a drain ofp-type silicon. A portion of the pillar-shaped silicon 101 surrounded bythe third metal 103 functions as i-type silicon, low-concentrationn-type silicon, or low-concentration p-type silicon. Thus, a p-typetransistor is provided.

As described above, transistor operation can be achieved without animpurity present in the pillar-shaped silicon. Therefore, impurityimplantation for forming a diffusion layer is not necessary.

A semiconductor device having an SGT structure according to anembodiment of the disclosure will now be described with reference toFIG. 2.

In a pillar-shaped semiconductor 201 disposed on a substrate 210, afirst insulator 211 surrounds a portion of the pillar-shapedsemiconductor 201 at an end of the pillar-shaped semiconductor 201, afirst metal 204 surrounds the first insulator 211, a fourth insulator212 surrounds a portion of the pillar-shaped semiconductor 201 at theend of the pillar-shaped semiconductor 201, a second metal 205 surroundsthe fourth insulator 212, a fifth insulator 202 surrounds a portion ofthe pillar-shaped semiconductor 201 in a region sandwiched between thefirst metal 204 and the second metal 205, a third metal 203 surroundsthe fifth insulator 202, a second insulator 207 is between the firstmetal 204 and the third metal 203, a third insulator 206 is between thesecond metal 205 and the third metal 203, a fourth metal 208 connectsthe first metal 204 and the one end of the pillar-shaped semiconductor201, and a fifth metal 209 connects the second metal 205 and the otherend of the pillar-shaped semiconductor 201.

A semiconductor device having an SGT structure according to anembodiment of the disclosure will now be described with reference toFIG. 3.

In a pillar-shaped semiconductor 301 disposed on a substrate 310, afirst insulator 311 surrounds at least a part of a portion of thepillar-shaped semiconductor 301 at one end of the pillar-shapedsemiconductor 301, a first metal 304 surrounds at least a part of thefirst insulator 311, a fourth insulator 312 surrounds at least a part ofa portion of the pillar-shaped semiconductor 301 at the end of thepillar-shaped semiconductor 301, a second metal 305 surrounds at least apart of the fourth insulator 312, a fifth insulator 302 surrounds atleast a part of a portion of the pillar-shaped semiconductor 301 in aregion sandwiched between the first metal 304 and the second metal 305,a third metal 303 surrounds at least a part of the fifth insulator 302,a second insulator 307 is between the first metal 304 and the thirdmetal 303, a third insulator 306 is between the second metal 305 and thethird metal 303, a fourth metal 308 connects the first metal 304 and thefirst end of the pillar-shaped semiconductor 301, and a fifth metal 309connects the second metal 305 and the second end of the pillar-shapedsemiconductor 301.

In the present invention, various embodiments and modifications can bemade without departing from the broad sprit and scope of the presentinvention. Furthermore, the above-described embodiment is provided todescribe one embodiment of the present invention, and the scope of thepresent invention is not limited thereto.

1. A semiconductor device comprising: a pillar-shaped semiconductorhaving an impurity concentration of 10¹⁷ cm⁻³ or less; a first insulatorsurrounding the pillar-shaped semiconductor; a first metal surrounding aportion of the first insulator at a first end of the pillar-shapedsemiconductor; a second metal surrounding a portion of the firstinsulator at a second end of the pillar-shaped semiconductor; a thirdmetal surrounding a portion of the first insulator in a regionsandwiched between the first metal and the second metal; a secondinsulator between the first metal and the third metal; a third insulatorbetween the second metal and the third metal; wherein the first metal iselectrically connected to the first end of the pillar-shapedsemiconductor, wherein the second metal is electrically connected to thesecond end of the pillar-shaped semiconductor, wherein the third metalhas a work function of about 4.2 eV to about 5.0 eV.
 2. Thesemiconductor device according to claim 1, wherein the semiconductorcomprises silicon.
 3. The semiconductor device according to claim 2,wherein the first metal and the second metal have a work function ofabout 4.0 eV to about 4.2 eV.
 4. The semiconductor device according toclaim 2, wherein the first metal and the second metal have a workfunction of about 5.0 eV to about 5.2 eV.
 5. A semiconductor devicecomprising: a pillar-shaped semiconductor; a first insulator surroundingthe pillar-shaped semiconductor; a first metal surrounding a portion ofthe first insulator at a first end of the pillar-shaped semiconductor; asecond metal surrounding a portion of the first insulator at a secondend of the pillar-shaped semiconductor; a third metal surrounding aportion of the first insulator in a region sandwiched between the firstmetal and the second metal; a second insulator between the first metaland the third metal; a third insulator between the second metal and thethird metal, wherein the first metal is electrically connected to thefirst end of the pillar-shaped semiconductor, wherein the second metalis electrically connected to the second end of the pillar-shapedsemiconductor.
 6. The semiconductor device according to claim 5, whereincharge carriers are induced at the first end of the pillar-shapedsemiconductor by a difference in a work function between thepillar-shaped semiconductor and the first metal, and carriers areinduced at the second end of the pillar-shaped semiconductor by adifference in the work function between the pillar-shaped semiconductorand the second metal.
 7. A semiconductor device comprising: apillar-shaped semiconductor; a first insulator surrounding a portion ofthe pillar-shaped semiconductor at a first end of the pillar-shapedsemiconductor; a first metal surrounding the first insulator; a fourthinsulator surrounding a portion of the pillar-shaped semiconductor at asecond end of the pillar-shaped semiconductor; a second metalsurrounding the fourth insulator; a fifth insulator surrounding aportion of the pillar-shaped semiconductor in a region sandwichedbetween the first metal and the second metal; a third metal surroundingthe fifth insulator; a second insulator between the first metal and thethird metal; a third insulator between the second metal and the thirdmetal, wherein the first metal is electrically connected to the firstend of the pillar-shaped semiconductor, wherein the second metal iselectrically connected to the second end of the pillar-shapedsemiconductor.
 8. The semiconductor device according to claim 7, whereincharge carriers are induced at the first end of the pillar-shapedsemiconductor by a difference in a work function between thepillar-shaped semiconductor and the first metal, and charge carriers areinduced at the second end of the pillar-shaped semiconductor by adifference in a work function between the pillar-shaped semiconductorand the second metal.
 9. A semiconductor device comprising: apillar-shaped semiconductor; a first insulator surrounding at least apart of a portion of the pillar-shaped semiconductor at a first end ofthe pillar-shaped semiconductor; a first metal surrounding at least apart of the first insulator; a fourth insulator surrounding at least apart of a portion of the pillar-shaped semiconductor at a second end ofthe pillar-shaped semiconductor; a second metal surrounding at least apart of the fourth insulator; a fifth insulator surrounding at least apart of a portion of the pillar-shaped semiconductor in a regionsandwiched between the first metal and the second metal; a third metalsurrounding at least a part of the fifth insulator; a second insulatorbetween the first metal and the third metal; a third insulator betweenthe second metal and the third metal, wherein the first metal iselectrically connected to the first end of the pillar-shapedsemiconductor, wherein the second metal is electrically connected to thesecond end of the pillar-shaped semiconductor.
 10. The semiconductordevice according to claim 9, wherein charge carriers are induced at thefirst end of the pillar-shaped semiconductor by a difference in a workfunction between the pillar-shaped semiconductor and the first metal,and charge carriers are induced at the second end of the pillar-shapedsemiconductor by a difference in a work function between thepillar-shaped semiconductor and the second metal.
 11. A semiconductordevice comprising: a pillar-shaped transistor having a gate, drain andsource electrode comprising work functions metals, wherein theelectrodes are partially or completely wrapped around a semiconductorpillar body, and wherein the electrodes are isolated from each other andfrom the semiconductor pillar body by dielectrics materials.